1. Field of the Invention
The current invention relates to measuring devices, and in particular, to devices that measure linear lengths, such as tape measures.
2. Description of the Related Art
Tape measures and rulers are devices that are used for measuring linear lengths of a variety of items. While a ruler is generally a marked, rigid, flattened stick-like object of fixed dimensions, a tape measure is flexible and can be extended to an almost infinite variety of lengths, up to a maximum length. A folding ruler, which comprises a plurality of sub-rulers movably connected together falls somewhere in between a ruler and a tape measure. Tape measures and folding rulers are, in essence, adjustable-length measuring devices. A tape measure typically includes a ribbon, i.e., “tape,” made of a flexible material, such as, e.g., metallic ribbon or fiber, where the tape is marked to indicate linear lengths. The tape measure may consist of just the tape, which can be rolled-up, folded, or otherwise compacted. Typically, however, the tape measure includes a housing which stores, rolled-up, the unused portion of the tape.
FIG. 1 shows a simplified perspective view of exemplary prior-art tape measure 100. Tape measure 100 comprises housing 101 and tape 102. Only the extracted portion of tape 102 is visible in FIG. 1, while the rest of tape 102 is rolled up inside housing 101. Tape 102 comprises zero mark 103 at a first edge of tape 102. Zero mark 103 is at length zero. Tape 102 is marked and labeled to indicate increasing linear lengths from zero mark 103. Typically, for American tape measures, the markings indicate lengths in inches and fractions thereof.
Zero mark 103 is accompanied by tab 104, which is orthogonal to tape 102 and which facilitates measuring from the edge of a solid object. Generally, tape measures may be used to measure any linear target, where a linear target is defined by two distinct points in space. Often, these two distinct points are opposing edges of a rectangular solid. To measure the length of such a linear target, tape 102 is pulled out of housing 101 to the extent needed to equal or exceed the length of the target, presuming tape 102 is at least as long as the target. Zero mark 103 is set substantially at the first point of the target, and the length marking on tape 102 is read at substantially the second point of the linear target, thereby providing the length of the linear target. This mode of measurement is referred to herein as regular mode.
In some situations, the linear target is a space between a first point and a second point, where the target can be measured by having zero mark 103 at the first point and far edge 105 of housing 101 at the second point, presuming tape 102 is long enough to have tape measure 100 span the distance. The distance between the two points is then determined by adding the width w of housing 101 to the measurement on tape 102 at near edge 106 of housing 101. This mode of measurement, which uses an offset w, is referred to herein as offset mode.
If a user of tape measure 100 wants to find a particular fractional length of a target length, then the user would measure the length of the target, then calculate the desired fraction of the length, and then would be able to mark that fractional length along the target. This system for determining fractional lengths of target lengths is cumbersome and may also be subject to errors from calculation errors and incorrect readings of measurements.